1. Field of the Invention
The present invention relates generally to switching power supply circuits and more particularly, to pulse width modulation systems for use in switching power supply circuits.
2. Background of the Invention
Switching power supply circuits are commonly used to convert an input AC or DC voltage or current to a different AC or DC voltage or current output. Such circuits typically include one or more switching devices (e.g., MOSFETs) and passive component(s) (e.g. inductors, capacitors) to convert energy from the input source to the output. It is known to use a pulse width modulation device to turn on and off the switching devices at a desired frequency. The pulse width modulation device regulates the output voltage, current or power delivered by the switching power supply circuit by varying the duty cycle applied to the switching devices.
Pulse width modulation devices such as these provide a simple, yet effective, tool for providing pulse width modulated signals with relatively precise durations and duty cycles and have been used in myriad applications, such as voltage regulation modules, DC/DC converters, and other electronic devices. To simplify the integration in conjunction with digital control systems, digitally-controlled pulse width modulation systems have been developed. These digitally-controlled pulse width modulation systems have been implemented in several forms, including as counters supplied by a high frequency clock, ring oscillators with a multiplexer together and with look-up tables.
As the desired resolution of the pulse width modulated signals continues to increase, existing digitally-controlled pulse width modulation systems have proven to be unsatisfactory in many respects. For example, high-resolution pulse width modulated signals provided by the digitally-controlled pulse width modulation systems can include waveform discontinuities and can lead to noise and oscillator sub-harmonics. Increased resolution also generally corresponds with very high oscillator frequencies, which can exceed one gigacycle.
In view of the foregoing, it is believed that a need exists for an improved pulse width modulation system that overcomes the aforementioned obstacles and deficiencies of currently-available pulse width modulation systems. More particularly, a need exists for high resolution pulse width modulation system for use in switching power supply circuits.